Python 2.7 : Write to file instantly

I realized that when I write into a file using python it wait until the end of my Python file to execute it:

outputFile = open("./outputFile.txt","a")
outputFile.write("First")
print "Now you have 10sec to see that outputFile.txt is still the same as before"
time.sleep(10)
outputFile.write("Second")
print "Now if you look at outputFile.txt you will see 'First' and 'Second'"